Conventionally, in the field of production for a printed wiring board, as a resist material used for etching, plating, and the like, photosensitive elements obtained by using a photosensitive resin composition, a supporting member and a protection film have been used widely.
The printed wiring board is produced by a method of pattern exposure of a photosensitive element laminated on a copper substrate, eliminating a uncured part with a developing solution, applying an etching or plating for forming a pattern, and eliminating the uncured part from the substrate.
According to the recent trend in favor of a higher density of the printed wiring boards, a high resolution and a high adhesive property are more and more required for the photosensitive element as compared with the conventional photosensitive element.
Moreover, from the viewpoint of the throughput, a high sensitivity is also highly required for the resist.
In contrast, according to a quick generation change of the electronic appliances such as cellular phones, an increase in cost for a mask per one substrate is concerned if the method for forming a resist pattern using the conventional phototool (photomask) is employed. A method for directly imaging a circuit produced by a CAD with a laser beam without the need of a mask (Laser Direct Imaging) is now appreciated.
As mentioned above, it is a characteristic of the LDI to provide many advantages such as efficient production ability by a small number and various kinds, elimination of a positioning step owing to absence of a photomask so as to facilitate correction of scaling, and elimination of any caution for sticking of photomask to photoresist.
According to the conventional laser using a visible light, handling operations had to be done in a dark room or under a red light. The present inventors have found out, by utilizing a laser using an ultraviolet ray, a laser exposing method allowing operations under an yellow light like the ordinary exposure can be realized. However, since a photosensitive resin composition for the ultraviolet ray laser is highly sensitive, there arise a problem such that the photosensitive property is fluctuated due to the light and the heat of the safety light including the yellow light, etc. accompanying the operations, so that the processability is limited.
Further, while the throughput depends on the laser scanning speed, it is still insufficient in terms of the above-mentioned throughput, therefore, propagation thereof is slower than expected. It is found out that the present problem does not reside in equipments but resides in an insufficiency of the sensitivity of the photosensitive resin composition so that an improvement of the scanning speed is prevented.
Additionally, in order to cope with the UV (ultraviolet ray) laser scanning exposure, an extremely highly sensitive resist with an excellent resolution is required so that it cannot be dealt with by the present resist.
The present invention is to solve the above-mentioned problems, and it is to provide a photosensitive resin composition for the laser scanning exposure with a little exposure amount fluctuation under a specific condition after a long term storage, thereby providing an excellent long term storage property and processability, and having an excellent resolution and laser imaging compatibility, in particular, an excellent ultraviolet ray laser imaging compatibility and color change stability after a long term storage.
Further, the present invention is to provide a photosensitive resin composition, a photosensitive element, a method for producing a resist pattern and a method for producing a printed wiring board having an excellent sensitivity, resolution, developing property and mechanical strength, effective for achieving a high density in a printed wiring board and laser exposure, particularly, the ultraviolet ray laser imaging compatibility.
Furthermore, the present invention is to provide a method for producing a resist pattern having an excellent-sensitivity, resolution, productivity and processability, effective for achieving a high density in a printed wiring board, and workable under a yellow light in a conventional clean room.